Presently, digital data communication devices, such as ISDN terminal adapters, provide at least one analog port which enables an analog device, e.g., a telephone, fax or a modem, to be interconnected to the terminal adapter. Terminal adapters are capable of receiving analog voice and/or voice-band data (fax, analog modem), converting it to digital form by means of a codec (coder/decoder), and transmitting the digitized voice/voice-band data over the digital network. Also, terminal adapters are capable of receiving digitized voice/voice-band data from the digital network, converting it to analog form with the codec and providing the analog to the analog device. There are typically a suite of single and dual tones, such as dial-tone, ring-back, busy and DTMF (Dual Tone Multi-Frequency), which provide information to the digital network and include information from the digital network, that must be either generated or detected by the analog device to provide standard analog voice, fax or data services.
Tones that are generated by the analog device include DTMF tones which correspond to the numbers 0-9 and the "*" and "#" symbols that may be dialed by the analog device in order to establish a connection with another device. When the analog device dials a telephone number, the tones corresponding to the number are received and decoded by the terminal adapter and then forwarded to the digital network switch, which may send an indication to the analog device regarding the connection status of the call via a network provided tone or announcement.
Tones that must be detected by the analog device include, e.g., the dial-tone, ring-back, and busy tones, which are monitored to determine connection status. The dial-tone is received by the analog device when it goes off-hook to place a call to another device. The ring-back tone is received by the analog device after it attempts to place a call to another device and that device is not busy. The busy tone is received by the analog device after it attempts to place a call to another device and that device is busy.
Present terminal adapters typically include a DTMF decoder which receives from the analog device the DTMF tones and outputs a digital representation of the tones to the microprocessor of the terminal adapter. The tones that the analog device must detect are either generated by the network or the network provides signals representing the tones and the terminal adapter must generate the tones. For example, in the US, ISDN networks generate the tones and the terminal adapter coverts the tones to analog with the codec and transfers the tones to the analog device through a hybrid circuit. In contrast, in Japan, ISDN networks do not generate the tones and therefore the terminal adapter must generate the tones. Typically, the terminal adapter must be capable of operating either way and depending on the type of network, must be configured accordingly.
In order to generate the tones, the processor of the terminal adapter includes in its memory tables, samples corresponding to the various types of tones that it must be capable of generating. Depending on the signal received from the network (e.g., dial-tone, ring-back. etc.), the appropriate samples are output from the processor to a digital-to-analog converter (DAC). The DAC converts the digital samples to analog and provides the analog signals (tones) to the hybrid circuit which passes the tones to the analog device. The analog device then responds accordingly based on the tone received.
In order for a terminal adapter to receive tones generated by the analog device and generate tones to be provided to the analog device, it must include, in addition to the codec, a DTMF decoder and a DAC. Hence there remains a need for a digital data communications device that can receive tones generated by the analog device and generate tones to be provided to the analog device without the need for additional hardware components, such as the DTMF decoder and the DAC.